THE CULTIVATION OF BACTERIA. 



77 



interior of the air-chamber, and often another into the water 

 standing in the water-jacket. A gas-regulator passes through 

 another hole, and is immersed in the water standing in the 

 water-jacket. There are various forms of gas-regulators more 

 or less complicated. In general they consist usually of a tube 

 containing mercury; into this tube are two openings, one 



Fig. 23. — ^Reichert's 

 Gas-reguxatoe. 



Fig. 24. — Mercurial Gas-regula- 

 tor. 

 a. Chamber containing volatile hy- 

 drocarbon. 6. CapiDaiy opening. 



for the entrance and the other for the exit of gas. The gas 

 enters through a small tube, which is cut off diagonally at 

 the bottom, and which projects into the surface of the mer- 

 cury. Heating the water in the water-jacket causes expansion 

 of the mercury, which rises, and, little by little, cuts o£f the 

 inflow of gas through this tube. The flow is never completely 

 cut off, as there is a capillary opening in the tube consider- 



